1. Field of the Invention
The invention relates to a method for joining an initial section of a film tube wound in a band-like manner on a reel with an end section of a second film tube, especially for packaging systems, and a packaging system.
2. Prior Art
Film tubes are usually wound up on reels which are held in a rotatable fashion and from which the film tube is unwound and supplied to further processing steps. The film tube is also designated below as a tube roll. Film tubes are used in packaging systems in numerous ways, e.g. in bagging systems for packing goods into bags or in palletizing systems for wrapping goods held on pallets.
In bagging systems for example, the film tube is wound off from such a tube roll and filled with material in subsequent sections of the machine. For this purpose it is necessary that the film tube which is present at first in a band-like manner needs to be opened in order to enable its filling. This occurs with the help of a mandrel which is positioned in the axial direction within the film tube, so that the film tube is opened when passing the mandrel. Such a configuration is also known as a “flying mandrel” because the mandrel needs to be held in the interior of the film tube in stable fixing. As an alternative to such a flying mandrel, it is also possible to use wedges or vacuum suction devices, especially when processing bags with slit folds.
The opening of the film tube produced with the help of the mandrel is now available for filling with goods in bagging systems or for wrapping goods in palletizing systems. In the case of bagging systems, the respective film tube section is sealed on either side of the filled material with the help of special welding methods for example, and the packaged goods can be removed.
There is a special problem-concerning the exchange of the reel when the film tube wound on the reel is completely used up. In a conventional manner, the packaging system is stopped, the reel of the consumed tube roll is removed and a new tube roll is made available instead. The initial section of the new tube roll is then inserted manually in a positioning and tensioning station downstream of the tube roll and is supplied to the next following sections within the system. In particular, the mandrel or wedge is manually inserted into the initial section of the new tube roll. The packaging system can only be started again when the mandrel or wedge has been inserted.
The change of a reel thus leads to longer standstill periods of the entire system. Notice must be taken that tube rolls usually comprise approximately 1200 bags. The processing speed of bagging systems is close to approximately 1800 bags per hour however. A tube roll is thus used up in approximately 40 minutes. The change of the tube roll takes about 10 to 20 minutes. The bagging system is thus at a standstill up to a third of its operating period during operation. Increasing processing speeds for film tubes lead to an increasing deterioration of the ratio between working time and standstill time of the system.
Therefore, it has been proposed not to wind up the film tubes on reels at the producer's side but to provide special containers in which the band-like packaging material is hold in a folded manner so that the second end of the band-like packaging material rests at least over some time and is accessible from the outside of the container during the first end is fed into the packaging system. This makes it possible to work with the second end and especially to join it with an end section of a band-like packaging material of a successive, second container during the feed of the first end. Thus, after the packaging material has been completely used up in the first container, withdrawal from the second container is automatically started. Already during start up of the packaging system two ends of packaging material which are located in two successive containers may be joined with each other so that depending on the number of available containers an arbitrary supply of packaging material can be provided without the need for stopping the packaging system.
For the folded storage of the band-like packaging material different possibilities have been proposed, e.g., in form of a pile in which two planes of the pile of the packaging material being each adjacent to a folding axis are lying basically horizontally upon each other. In this case, the first end of the band-like packaging material may be adjacent to the upmost plane of the pile, and the second end of the band-like packaging material may be adjacent to the bottom plane of the pile, so that starting with the end of the packaging material which is fed to the processing system the material is taken from the upper areas of the pile. The end which is at last fed to the processing system may, e.g., be pulled from the bottom along a side wall of the container to the area of the uppermost plane of the pile from where it may project over the upper bounds of the container. Alternatively, an opening may be provided in the bottom area of the container for taking out the second end section. These measures are only feasible in cases where the band-like packaging material is indeed provided in a folded manner.
EP 1 201 585 A1, therefore, proposes to cut the initial section of a new tube roll in a trapezoid manner, to place the tab thus formed over the end section of an old tube roll, which end section has not been cut in any way, and to join the two sections. Since, according to EP 1 201 585 A1, the end section of the old tube roll is not cut in a trapezoid manner for the formation of swivelable tabs, the formation of a tension-proof connection, e.g., by welding, can only occur, if a support is provided inside the downstream film tube. This support, however, must be held in place inside the downstream film tube for which purpose guiding rolls are provided in EP 1 201 585 A1. A setting of this kind where a support permanently guided by guiding rolls is provided inside the film tube, however, has at least two significant disadvantages. First, in particular the guiding rolls inside the downstream film tube need lubrication, so that application of a method according to EP 1 201 585 A1 is questionable for, e.g., bagging systems for food or feed. Secondly, a method according to EP 1 201 585 A1 considerably limits the speed of the film band, since the heat transfer to the support guided inside the downstream film tube would otherwise be too big. In particular, the plasticity limit of plastics usually used for film tubes would be reached locally, so that, e.g., during a stop of the film undesired weldings between the support or its guiding rolls and the film would be inevitable.
It has, therefore, already been proposed to form a tab by placing a cut at the initial section and the end section, which can be flipped open and each of which is arranged in the region of the longitudinal axis, i.e. in the central region of the respective film tube. The tabs are placed above each other and joined in a tension-proof way. The welding anvil necessary for establishing a tension-proof joint by welding must be slid laterally into the central regions of the film tubes to be joined in order to place the centrally arranged tabs and to enable the same to be welded.
In order to produce such tabs, it is necessary that the boundary regions are cut in an oblique way relative to the longitudinal axis of the film tube, so that the initial and end section taper at the end side, e.g. in a trapezoid manner. Such a type of connection can, in principal, be applied to any kind of film tube, however, disadvantages can occur especially in tubes with side folds because tubes with side folds often use so-called side wedges. These side wedges engage in the side folds and are used for widening the film tube. In the type of connection thus described it may occur, as a result of the formation of gaps in the boundary regions of the film tubes, that the side wedges unthread at the joining points.